A wind power plant, also referred to as wind farm, comprises a plurality of wind turbine generators that convert the kinetic energy of the wind into electricity. The collective contributions of all the wind turbine generators amount to the power production of the wind power plant.
The problems associated with the production of electricity in a wind power plant are significantly different from that of other conventional power plants, such as those powered by coal or gas.
First of all, the natural source used in each case has very different behavior. Wind is an intermittent and unpredictable resource, which results in uncertainty about whether the active power production of the wind power plant at a given time is able to cope with an also variable target demand.
Secondly, while in conventional power plants the turbine generators are synchronous machines directly coupled to a power grid, the wind turbine generators may be asynchronous and usually have power converters decoupling the generator from de grid.
A wind power plant is typically connected to a power grid, where other power plants and loads are also connected. The unbalance between the power produced by all power plants and the power demanded by the loads results, for example, in frequency drifts of the voltage, which further complicates the delivery stable power to the grid.
To control electrical variables at the point of connection to the grid the wind power plant requires the use of a regulator.
Some attempts to regulate the electrical variables of a wind power plant operatively connected to a power grid have focused only on regulation of the active power produced by the plant, such as for instance the regulators disclosed in patent publications WO2012/019609 and EP1571746.
Some other attempts have been directed to the regulation of the reactive power loop. In that sense, US2010/0312409 discloses a wind park in which two electrical variables related to the reactive power, namely power factor and voltage, are simultaneously controlled.
In order to make the operation of a wind power plant similar to that of a conventional power plant, simultaneous regulation of the active power loop and of the reactive power loop would be needed.
However, simultaneous regulation is not simple because control modes used in a given regulation loop have a direct effect on the other regulation loop. For instance, power factor control mode or apparent power limitation used in the reactive power regulation loop depend directly on the active power production. Also, the power produced by the wind turbine generators is related to the reactive power capability production through their PQTV curves. Furthermore, active power has an impact on voltage value at grid connection point when the short circuit ratio of the grid is low, or the resistance-to-reactance ratio is high.
Furthermore, user, transmission system operators, or country regulations may require different control modes to be implemented in either the active power regulation loop or in the reactive power regulation loop, or even different control modes being selected at different times.
Some solutions offer some flexibility in the way how an electrical variable of a wind power plant is regulated by allowing the operator to select a control mode.
For example, EP2375562 discloses a wind turbine generator system that comprises two regulators, one that regulates the reactive power and another that regulates the power factor, connected to a control switching unit that allows selection of one of the two control modes. Despite providing some flexibility, this solution only provides a control mode at any given time.
Also, US2011/0148114 discloses a system for operating a wind power plant in which regulation of an electrical variable of the wind power is defined by a model selected from a number of models.
It is an object of the present invention to provide a system and method that can set up, commission and operate a wind power plant so that it behaves like a conventional power plant providing the transmission system operator, or the end users, with the same quality of service as that provided by conventional power plants.
It is another object of the present invention to provide a system and method to operate a wind power plant that allows for simultaneous regulation of the active power loop and the reactive power loop.
It is yet another object of the present invention to present a system and method that makes it possible to operate the wind power plant with higher flexibility and adaptability.